Here is a list of food considered safe for rabbits to eat. Although these are safe, they should be introduced to your rabbits diet gradually, one at a time. If a particular food causes your rabbit to produce runny droppings, eliminate it from their diet.
It is best to keep it simple, find a few veg and a couple of fruits that your bunny enjoys with no adverse effect and stick to these. Make sure one of these contains vitamin A... We've yet to find a rabbit that didn't like carrots!